Endorsement-contract dispute brings track star sudden popularity

EUGENE, Ore.—Boris Berian punched his ticket to the Rio Games at the U.S. Olympic track and field trials and spent the weekend signing autographs and posing for photos with fans.

It was a scene that few expected earlier this year. But the little-known runner has become a celebrity since an unusual lawsuit by Nike Inc. accused Mr. Berian of breaching an endorsement contract by competing in New Balance sneakers. Nike had sought to stop...